TABLE 2.
Classification performance, subgroup, and sensitivity analyses.
| Section | Configuration | N (PD/LBD) | N (FTD/Group 2) | N Total | Mean age PD/LBD | Mean age FTD | Residual age gap (y) | AUC | 95% CI | Sensitivity | Specificity | Notes |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| A. Progressive inclusion | k = 2, all intervals | 385 | 744 | 1,129 | – | – | – | 0.785 | 0.757–0.814 | – | – | |
| A. Progressive inclusion | k = 3 | 385 | 371 | 756 | – | – | – | 0.812 | 0.777–0.843 | – | – | |
| A. Progressive inclusion | k = 4 [threshold] | 196 | 195 | 391 | – | – | – | 0.831 | 0.791–0.873 | – | – | Apparent diminishing-returns threshold |
| A. Progressive inclusion | k = 5 | 77 | 103 | 180 | – | – | – | 0.856 | 0.789–0.914 | – | – | Wide CI; overlaps k = 4 |
| A. Progressive inclusion | k = 6 | 32 | 66 | 98 | – | – | – | 0.846 | 0.739–0.933 | – | – | Wide CI; exploratory |
| B. Interval strata (k = 2) | 6–12 months | 137 | 94 | 231 | – | – | – | 0.837 | 0.787–0.885 | – | – | Minimum viable assessment |
| B. Interval strata (k = 2) | 12–18 months | 192 | 471 | 663 | – | – | – | 0.837 | 0.800–0.872 | – | – | |
| B. Interval strata (k = 2) | 18+ months | 56 | 176 | 232 | – | – | – | 0.731 | 0.654–0.803 | – | – | Survivorship bias likely |
| C. Subgroups (k = 2) | bvFTD vs. PD/LBD | 385 | 95 | 480 | – | – | – | 0.771 | 0.718–0.824 | – | – | Subgroup |
| C. Subgroups (k = 2) | PPA vs. PD/LBD | 385 | 126 | 511 | – | – | – | 0.807 | 0.757–0.852 | – | – | Subgroup |
| D. Sensitivity analyses | Primary k = 2 | 385 | 744 | 1,129 | 70.6 | 58.4 | 12.2 | 0.785 | 0.757–0.814 | 0.922 | 0.525 | |
| D. Sensitivity analyses | Age-matched (caliper 2 y) | 336 | 336 | 672 | 68.7 | 69.0 | −0.3 | 0.794 | 0.761–0.826 | 0.729 | 0.714 | |
| D. Sensitivity analyses | Age-restricted (55–75 y) | 269 | 445 | 714 | 67.2 | 64.6 | 2.6 | 0.777 | 0.741–0.814 | 0.84 | 0.591 | |
| D. Sensitivity analyses | Age-only | 385 | 744 | 1,129 | 70.6 | 58.4 | 12.2 | 0.721 | 0.691–0.751 | 0.599 | 0.761 | |
| D. Sensitivity analyses | Slopes + age | 385 | 744 | 1,129 | 70.6 | 58.4 | 12.2 | 0.867 | 0.845–0.888 | 0.724 | 0.86 | |
| D. Sensitivity analyses | Phenotyped-FTD-only | 385 | 233 | 618 | 70.6 | 62.8 | 7.7 | 0.799 | 0.763–0.834 | 0.605 | 0.836 |
AUC, area under the receiver operating characteristic curve; CI, confidence interval; bvFTD, behavioral variant frontotemporal dementia; PPA, primary progressive aphasia; PD/LBD, Parkinson’s disease or Lewy body dementia; FTD, frontotemporal dementia. Sensitivity denotes FTD detection and specificity denotes PD/LBD detection at the Youden-optimal operating point. Age-matched analysis used 1:1 nearest-neighbor matching on baseline age with a 2-year caliper (deterministic greedy, fixed order). Phenotyped FTD was defined by first-visit NACC-derived FTLDSUBT values 1, 2, or 3; all other, unknown, not-assessed, or missing values were excluded from the phenotyped-FTD-only analysis.